1. Field of the Invention
The present invention relates to a spectral characteristic correction apparatus, a spectral characteristic correction method, and a recording medium on which spectral characteristic correction program is recorded for correcting spectral characteristics characterizing a color signal including multiple chrominance signals.
2. Description of the Related Art
It is known that color reproduction of a subject shot by an image pickup apparatus such as a digital camera in different environments can vary between the environments. In reality, color reproduction also can vary even when the same subject is shot in the same environment.
Image pickup apparatuses are designed to pick up images by using an image pickup device equipped with a color filter, for example. Different types of image pickup devices have different characteristics, such as spectral characteristics, related to color reproduction. Characteristics of image pickup devices of the same type also can vary depending on materials and manufacturing processes of the image pickup devices or can change with time. The differences in characteristics result in color reproductions that vary from one image pickup apparatuses to another. Color reproduction is treated as one of important factors especially in medical fields. Differences in color production can inhibit medical diagnosis.
To solve the problem, various color correction techniques have been developed. For example, a technique that uses a fixed color correction coefficient that is independent of individual image pickup apparatuses to perform color correction has been proposed. Also, a technique that adaptively derives a color correction coefficient for each individual image pickup apparatus has been proposed.
To address this, for example Japanese Patent Application Laid-Open Publication No. 2001-358960 describes a technique that derives, on the basis of first and second spectral sensitivity distribution, a color correction coefficient for linearly converting a signal characterized by the first spectral sensitivity distribution to a signal characterized by the second spectral sensitivity distribution.
Japanese Patent Application Laid-Open Publication No. 2005-117524 describes a technique in which a color chart is photographed for each of multiple image pickup devices and a color correction coefficient is derived such that image data of the photographed color charts agree with each other.
With the technique described in Japanese Patent Application Laid-Open Publication No. 2001-358960, an optimum color correction coefficient that accommodate differences between two spectral sensitivity distributions can be derived since a color correction coefficient is derived on the basis of each spectral sensitivity distribution.
In the technique described in Japanese Patent Application Laid-Open Publication No. 2005-117524, which uses image data of a color chart photographed with an image pickup apparatus to derive a color correction coefficient, the derived color correction coefficient depends on the number of colors on the color chart.